WASHINGTON (AP) — The 10 U.S. sailors captured and humiliated by Iran after mistakenly steering their boats into Iranian waters in January were beset not just by poor judgment and faulty equipment.

They also showed a remarkable lack of curiosity about potential dangers in one of the world’s more dangerous waterways, according to an in-depth Navy investigation.

In deviating from their planned Persian Gulf route from Kuwait to Bahrain – without asking approval or notifying superiors – they passed an island to their east and wondered whether it might be Saudi territory, rocks or oil platforms. The crews of both boats consulted their navigation systems, which depicted the mass as a small purple dot.

Despite being unsure of their surroundings, the sailors did not adjust their onboard navigation displays to enlarge the purple dot; if they had, they would have seen that it was labeled Farsi Island, a well-known base for the Iran Revolutionary Guard Corps Navy.

“No crewmembers on either (boat) utilized a paper navigational chart in order to plot their exact location or to identify the island they had seen, even though the charts were available” on their boats, known as Riverine Command Boats, the investigation report said. No crewmember even bothered to log the fact that they had seen the island.

“Crewmembers lacked navigational awareness, proper communication with higher authority, and appreciation of the threat environment throughout the transit,” the report said.